The transfer case containing the remains of U.S. Marine Cpl. Richard Rivera, is moved by a U.S. Marine carry team during a dignified transfer at Dover Air Force Base in Dover, Del., Aug. 13, 2012. Cpl. Rivera who was from Oxnard, Ca. was killed on August 10th while supporting combat operations in Helmand province, Afghanistan.

“Just don’t talk about the war!” was the motto evinced by John Cleese’s comic British innkeeper Basil Fawlty when entertaining German tourists at his establishment. The same motto seems to have been embraced by both candidates in the 2012 U.S. presidential election — and not simply because it’s difficult to detect significant differences on their policies for ending the longest war in America’s history. Neither President Barack Obama, nor Governor Mitt Romney can offer the electorate the prospect of a plausible outcome in Afghanistan that won’t leave many Americans wondering what was achieved in 11 years of a war that this week claimed its 2,000th American combat casualty. Opinion polls routinely find a substantial majority of Americans opposed to remaining militarily engaged in Afghanistan, which may be why the bipartisan consensus envisages most U.S. troops coming home by the end of 2014, handing security responsibility to the Afghan forces whose training and mentoring is rapidly becoming the mission’s prime focus. The Taliban won’t be defeated by the time the U.S. leaves, in other words, and it takes a leap of faith to envisage Afghan security forces finding the political will to fight the Taliban on behalf of a widely discredited Afghan regime once the U.S. leaves — and that was before the emergence of what the U.S. military calls a “systemic problem” of uniformed Afghans turning their weapons on their U.S. and NATO mentors. Afghanistan, for U.S. presidential campaign purposes, is a huge downer.

At least 40 times this year alone, U.S. and NATO soldiers have been killed by gunfire from allied security personnel in ostensibly safe bases. And the scale of of “green-on-blue” violence — although the Pentagon now prefers “insider attacks” — is difficult to determine, because such attacks are only reported when Western personnel are killed.

Insider attacks, deemed a “systemic problem” by the Pentagon, have already killed 23 Americans this year. And the vulnerability of Western troops is expected to actually increase in the coming months as a combat mission continues its transformation into one that deploys smaller groups of U.S. and NATO troops to mentor Afghan forces, exposing them to greater risk of attack from uniformed Afghans.

President Obama briefly addressed the issue last Monday, citing efforts to confront the phenomenon through improved intelligence and vetting of Afghan forces, and giving some U.S. personnel — “guardian angels” — the task of guarding others working with Afghan forces. California congressmen Duncan Hunter has called on the House Armed Services Committee to discuss the issue — but it’s an uncomfortable conversation because it hints at what may be fundamental flaws in the premise of the U.S. exit strategy, and perhaps even of the war started by President George W. Bush and escalated by Obama.

“It’s becoming obvious that the American people no longer have a clear sense of what we are trying to accomplish, why it remains necessary and how far we are from attaining our goal,” Virginia Republican congressman Frank Wolf told the Huffington Post. “We believe Congress has a moral obligation to convene hearings that will explore what has brought us to this point and how we can move forward as a nation in a sustainable way, honoring the tremendous sacrifice that has already been made by so many.”

It’s generally recognized across the board, now, that the Taliban won’t be militarily defeated, nor is there any immediate prospect of a political solution to the conflict. It’s politically difficult for the U.S. to offer concessions that might tempt the Taliban, which recognizes that the U.S. has reached the limit of its military commitment in Afghanistan. And the movement’s long-time backers in Pakistan’s security establishment are unlikely to press the Taliban into talks unless Pakistan’s interests in a future regime in Kabul are accommodated.

So, the U.S. will leave Afghanistan locked in the throes of the same civil war that was underway when it first invaded in late 2001, albeit with the scoreboard having been reversed: The Taliban is now the insurgent force, while its erstwhile enemies, the Northern Alliance, form the basis of the regime in Kabul. But whether that balance remains depends on the Afghan forces trained, equipped and funded by the U.S. and other international donors for the foreseeable future. Their numbers are far bigger than what Kabul could sustain on its own. But getting the Afghan military on its feet is not simply a question of training, equipment and funding. It is fundamentally a question of politics—Afghan politics over which Washington has little influence.

“The United States military often tends to behave as though you can create an effective allied military by just running them through the right number of training courses, giving them the right number of weapons, paying salary in sufficient amounts to raise a large enough force,” warns George Washington University professor Stephen Biddle. “But success and failure in building a third-world military, which is essentially what we are trying to do in Afghanistan, usually turns on soft questions like politics, whether the military in question gets captured by cronyism and politicized–and in this case, whether the politics of their relationship with their mentors works.”

It’s not hard to see how that relationship is poisoned if U.S. personnel suspect their Afghan charges could, at any point, shoot them in the back. The resultant wariness among American trainers towards their Afghan charges becomes a vicious circle, warns Andrew Exum, a former Army Ranger and consultant to the U.S. military in Afghanistan. “The Afghans must surely sense the Americans and other Westerners do not fully trust them, and it would only be natural for them to respond to that mistrust in kind.” One result Exum predicts is that U.S. personnel will be more inclined to trust ethnic Hazaras and Tajiks, traditionally supporters of the anti-Taliban Northern Alliance, rather than Pashtuns, the largest ethnic group in Afghanistan but also the social base of the Taliban. That will only reinforce long established tensions within the Afghan security forces, threatening the viability of those security forces after the U.S. leaves. (Relying on non-Pashtuns to fight the Taliban in the Pashtun heartland of southern and southeastern Afghanistan is, in the long-term, a losing strategy.)

That would be exactly why the Taliban would infiltrate supporters to conduct this kind of attack. U.S. forces believe infiltration is only a small part of the problem, although outside analysts believe it might be higher — and the Taliban is certainly claiming credit. But there appear to be other grievances at work, as well, and friction between Western troops and their Afghan charges. Gen. John Allen, U.S. commander in Afghanistan, on Thursday even cited the impact on soldiers’ mindset of the fact that the Ramadan fast fell during the fighting season this year as a contributing factor.

While Exum and others suggest that it would be easier to deal with Taliban infiltration, which is a counterintelligence challenge, the fact is that neither explanation offers much comfort, and has dimmed Western enthusiasm for the war — prompting NATO partners such as France and New Zealand to expedite their own withdrawal.

Nobody’s expecting the Afghan force that takes control in 2014 to take the fight to the Taliban. “It is unlikely that they are going to be able to drive the Taliban out of strongholds that the Taliban control at the time of handoff in 2014,” warns Biddle, who sees the best case as Afghan security forces managing to hold the ground taken from the insurgents by NATO forces. “The war is going to be in a condition of long-term stalemate as of 2014,” he warns, “and what that means is that the U.S. Congress is going to be asked to write multi-billion-dollar-a-year checks to keep this war going for a long, long time.” Whether or not Washington will remain willing to fund Afghanistan’s security after most U.S. troops leave remains an open question — and not one that’s likely to be discussed on the presidential campaign trail.

Tony Karon is a senior editor at TIME, where he has covered international conflicts in the Middle East, Asia, and the Balkans since 1997. A native of South Africa, he now resides with his family in Brooklyn, New York.